Hi Matthew. I'm currently in the states travelling. My emails are very back logged at the moment. I'd recommend you make a post in the forums, http://forums.sketchup.com/ - as I'm not likely to have much time until I'm back home next month.
There are plenty of skilled SketchUppers which I'm sure will be able to answer your questions.
(It's also my preferred way to answer questions - publicly in forums so other people can benefit and even propose a better answer than what I can muster up.)

Hi,
I'm seeking to install Cleanup3 but when I try to install it I get the error message:
" This extension has not been marked as being compatible with your version of SketchUp. You may experience usability issues if you try to install this extension."
I am using Sketchup 2014 which it says is supported, on a Mac with OSX 10.9.5. I'd welcome any suggestions as to why I'm getting this message and how I can install the extension.
Thanks,
Cathie

Some times SketchUp there are some small items that doesn't really "fix". These are not easy to detect. Just ignore them. When the number of fixed items doesn't change any more then CleanUp has done what it can.

The core.rb file hasn't been installed correctly. How did you install it? The preferred method is to use Extension Warehouse from within SketchUp to install it. Alternativly, download the RBZ and use Preferences > Extensions > Install Extensions.

Your error, showing that the core.rb file is located directly in the root of the Plugins folder - which I've only seen before when people used ZIP utilities that extracted without preserving sub-folders. Though I see you use SU2014 - so I'm surprised if you'd done that.

I do not recall installing "core.rb" at all. I just uninstalled/reinstalled SketchUp and deleted all associated folders, yet when I opened the reinstalled version, the error message was still present. I am currently searching my computer for this file so I can remove it and start from scratch. Any further ideas?

Thanks

update: for some reason I could not see the files listed in the error message. After copy/pasting I was able to see and delete those files and so I am hopeful the new reinstall will take care of the problem.

Installing was no problem, but I get a black overview when clicking settings by menu, "clean". I use sketchup 8. This way I can't change the settings. Clean with last settings does work though, but I don't know what settings are default. Can you help?

SketchUp use the Internet Explorer engine for the WebDialogs - which is why I'd like to know what version of IE you have installed. What browser you use for surfing website isn't relevant in this case.

Can you open the Ruby Console (under Window menu) before trying to open the CleanUp UI? Post back any errors.
Also, can you post a screenshot of the window? (You can post on the SketchUp forum: http://forums.sketchup.com/)

It would be the same as in the older versions of SketchUp.
How did you install it, via Extension Warehouse from within SketchUp or did you download the RBZ and try to install manually?
Did you also make sure to install TT_Lib?

Can you provide some more info?
What have you tried? Where does it fail?
Windows or OSX?
What SketchUp version?
Did you try to install directly from Extension Warehouse in SketchUp? Or did you use a browser to download the RBZ?
Did you install the required TT_Lib2? Linked in the description and should pop up a message if missing.

I imported DXF from Corel X7, the result itself was inexact cause of rounded edges.
Anyway, less work than drawing new completely, but after running cleanup with serveral settings the selection either disappeared or the selection is still a collection of disconnected lines, so that i have to define at least one line to close the figure. (same works without cleanup)
I understood CU3 as ->select figure ->run cleanup = well defined planar surface, or am i wrong?

Great idea! But my Material window locks up after using it. I can close and reopen it but the controls within it remain locked. The up/down slider, clicking on a material, switching from textures to colors, etc are all frozen. Any ideas?

Edit: I can chooose a material from the Materials window and apply it to a face, but it does not apply the material that I chose. It seems to randomly select a different texture each time.